Expansible chamber devices – Displacement control of plural cylinders arranged in... – Adjustment means includes external axially extending...
Patent
1982-06-21
1985-01-15
Garrett, Robert E.
Expansible chamber devices
Displacement control of plural cylinders arranged in...
Adjustment means includes external axially extending...
92 29, 92 32, 92 33, 92 63, 92129, 92165PR, 188196P, F01B 900
Patent
active
044932464
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
This invention concerns an air released, spring-applied brake cylinder of the type comprising a service or "duty" piston operated by the pressurized fluid, and a spring-applied brake piston (for the parking and/or emergency brake system), held in the "off" position by the pressure of the fluid acting in opposition to the reaction effort of the spring.
Existing spring type brakes comprise braking devices of the type in which a compressed-air service or "duty" brake is combined with a spring-applied brake, held in the "off" position by air pressure while the vehicle is in motion. A part from the risk of the spring-applied brake coming into action accidentally, if the air-pipe to the spring cylinder breaks, the main drawback of these combined brake systems, which otherwise offer very satisfactory regulation possibilities for the duty brake, lies in the fact that the reaction force of the spring operating the parking and emergency brake decreases rapidly as the spring is released. The distance the spring travels is often considerable, in order to take up the inevitable clearances that exist in the brake gear and between brake linings and brake surfaces, as well as the elasticity of the brake gear, as a result of the considerable forces which the linings exert on the brake surfaces. In many cases, it has been found, after several years' service, that the reaction force of the spring in such brakes, reduced by corrosion and creep affecting the spring steel, which remains under stress, reaches only between half and a third of the initial maximum design force, when in the braking position.
SUMMARY OF THE INVENTION
Methods of overcoming such drawbacks include avoiding keeping the spring under continuous compression. This has already been done, but is dangerous in that it reduces the reliability of the emergency braking system. Another method is to limit the travel of the spring when activated to apply the parking and/or emergency brake.
One of the purposes of this invention is to make more effective use of the reaction force of the prestressed spring, as known in the prior art, by using a nut threadedly fixed on the duty brake piston rod and having a clutch face engageable with a closely spaced, complimentary face of the spring piston to lock the nut against rotation in order to apply the spring brake force. Another purpose is to provide a brake cylinder comprising a duty brake piston and a spring-loaded brake piston, acting on the same brake gear, by means of a clearance adjuster common to both pistons, the said system forming a compact, reliable and inexpensive unit.
Accordingly, this new brake cylinder comprises a fluid-pressure actuated, spring-returned duty brake piston and a spring-actuated, fluid-pressure released parking and/or emergency brake piston. The spring piston is capable of transmitting all or part of the spring reaction force to the brake gear through a transmission surface on the spring-actuated parking brake piston, which is engageable with a nut member screwed to a screw-rod attached to the duty piston. The nut is held against a stop, which is to a certain degree fixed in relation to the cylinder casing, to thereby keep the nut, regardless of axial movements of the duty piston, at a short distance from the transmission surface, when the spring piston is in the extreme retracted position, under the effect of the releasing pressure, so that subsequent axial movement of the spring piton from its retracted position under the force of the actuating spring, by a distance greater than the said short distance, brings the transmission surface into contact with a corresponding contact surface on the nut, and locks it axially in relation to the screw-rod. The screw-rod is screwed on to another "take-up" nut on a duty brake piston clearance adjuster, this take-up nut being fixed, at least in the brake-operating position, to a rod which transmits the brake operating force.
The screw-rod, which must be carefully made from a tough material such as hardened steel, therefore co-o
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Girling Car Brake Actuation Equipment, Lucas Girling Limited, England, 8/1/79.
Falce G. J.
Garrett Robert E.
Meyer Richard S.
Wabco Westinghouse Equipements Ferroviaires
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